windows,windows\svc,windows\svc\mgr: use unsafe.Slice instead of unsafeheader.Slice

unsafe.Slice is available since Go 1.17, which is already the minimum
version supported by this package.

This change removes the dependency on the internal unsafeheader package,
which can be removed from the module.

Change-Id: I6c34cb152f2336ea04c5f9c7e88797ed8914f9cc
Reviewed-on: https://go-review.googlesource.com/c/sys/+/526635
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

windows/syscall_windows.go

@@ -15,8 +15,6 @@ import (
 	"time"
 	"unicode/utf16"
 	"unsafe"
-
-	"golang.org/x/sys/internal/unsafeheader"
 )
 
 type Handle uintptr
@@ -1667,12 +1665,8 @@ func NewNTUnicodeString(s string) (*NTUnicodeString, error) {
 
 // Slice returns a uint16 slice that aliases the data in the NTUnicodeString.
 func (s *NTUnicodeString) Slice() []uint16 {
-	var slice []uint16
-	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&slice))
-	hdr.Data = unsafe.Pointer(s.Buffer)
-	hdr.Len = int(s.Length)
-	hdr.Cap = int(s.MaximumLength)
-	return slice
+	slice := unsafe.Slice(s.Buffer, s.MaximumLength)
+	return slice[:s.Length]
 }
 
 func (s *NTUnicodeString) String() string {
@@ -1695,12 +1689,8 @@ func NewNTString(s string) (*NTString, error) {
 
 // Slice returns a byte slice that aliases the data in the NTString.
 func (s *NTString) Slice() []byte {
-	var slice []byte
-	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&slice))
-	hdr.Data = unsafe.Pointer(s.Buffer)
-	hdr.Len = int(s.Length)
-	hdr.Cap = int(s.MaximumLength)
-	return slice
+	slice := unsafe.Slice(s.Buffer, s.MaximumLength)
+	return slice[:s.Length]
 }
 
 func (s *NTString) String() string {
@@ -1752,10 +1742,7 @@ func LoadResourceData(module, resInfo Handle) (data []byte, err error) {
 	if err != nil {
 		return
 	}
-	h := (*unsafeheader.Slice)(unsafe.Pointer(&data))
-	h.Data = unsafe.Pointer(ptr)
-	h.Len = int(size)
-	h.Cap = int(size)
+	data = unsafe.Slice((*byte)(unsafe.Pointer(ptr)), size)
 	return
 }